30 Hour Work Weeks. Everyone works 3/4 time.
Instead of hiring six employees to work 240 hours per week, an employer could hire eight employees to work 240 hours per week. All those extra jobs will put a huge dent in unemployment.
Those eight employees have the equivalent of an extra day off and 30 extra minutes per day to exercise, cook dinner and spend time with family and friends, thereby making our society healthier and happier.
Edit: Forgot to mention that productivity generally rises as hours decrease.
I knew I wasn't the first one to think of this, but here's an article discussing it much more eloquently.